This invention relates to packing and particularly resilient U-ring type packing having a particular structured lip configuration which achieves a high degree of sealing with desirable wearing and friction characteristics.
Packing in the shape of an annular ring with a concentric recess or cavity on one surface is widely utilized as packing or sealing material for reciprocating rods, pistons, plungers, or cylinders driven by high pressure fluids. These concentrically recessed packing rings, conventionally described as U-rings, where the cross sectional contour of the cavity is U-shaped provide excellent automatic sealing in dynamic applications. Due to their geometrical shape and resilient nature, they are highly sensitive to pressure changes and insure a complete seal at raised operational pressures and quickly resume their initial or uncompressed shape or configuration under reduced pressures so as to maintain both friction and wear at a minimum.
While these ring shaped packings are of superior utility as packing-sealing material in a variety of dynamic applications, they nevertheless suffer from certain limitations or drawbacks which adversely inhibit their full desired utilization. Foremost of these are either a loss or leakage of the high pressure fluid past the packing and/or undesirable wear and friction characteristics at the surface in contact with the moving cylinder or piston. Generally, these disadvantages result from certain compromises made in the design and construction of the typical U-ring packers.
In operation under elevated pressure conditions the contact surfaces of the U-ring are forced securely against the stationary gland wall and the moving rod surface or the surface of the cylinder when used on a moving piston through the assistance of the high pressure fluid flowing into the U-shaped cavity of the ring. Under low pressure conditions the sealing is primarily achieved through the resiliency and configuration of the U-ring which force the contact surfaces expansively against the rod or the cylinder and gland wall to prevent leakage of the high pressure hydraulic or pneumatic fluid. Typically, such sealing and resiliency is provided by fabricating the U-ring of resilient material and extending the leg-lip portions of the ring upwardly and outwardly which, upon compression within the gland, attempt to resume their original or uncompressed shape and force outwardly against the rod or cylinder and gland wall. Under normal operation, the resiliency of the leg-lip portions tends to deteriorate after a period of time so that poor sealing is achieved particularly under low pressure operation.
To eliminate this deterioration and to maintain the desired sealing, various techniques have been employed. One conventional procedure involves inserting a separate elastomeric element for example an O-ring into the U-shaped cavity which, upon compression within the gland, increases the pressure on the legs or sealing lips so as to force them outwardly against the gland wall and rod surface to achieve the desired sealing. This separate elastomeric element however, fills a portion of the U-shaped cavity, thereby, reducing the amount of fluid introduced into the cavity under high pressure conditions, and tends, under low pressure conditions, to create an excessively high pressure on the sealing lips resulting in poor wear characteristics and undesirable friction. Another conventional means employed to improve the U-ring sealing characteristics under low pressure operation involves placing a mechanical device such as a spring within the U-shaped cavity to force the legs of the U-ring outwardly apart and thus achieve the desired sealing. These mechanical devices, however, have a tendency of becoming quickly fouled by the high pressure fluid and their useful life is generally very short.
Accordingly, an object of this invention is to provide an improved U-ring packing having desirable sealing properties over the entire operating pressure range with desirable wear and friction characteristics. Another object is to provide such U-ring packing with a lip configuration or structure which provides desirable resilient sealing while simultaneously maintaining the desired U-shaped cross sectional contour of the cavity. A further object is to provide a U-packing having such sealing characteristics which does not require or utilize separate elements within the cavity. These and other objects of this invention will be apparent from the following further detailed description thereof, together with the attached drawings.